A reprint of a lecture on the logic and rhetoric of threats and ultimatums — the language of diplomacy — delivered by the author on March 10, 1959. Whether it is called blackmail or deterrence, the art of influencing another's choice among alternatives by the use of threats is coercion. To provide a framework for representing and comparing alternatives, a game is developed, employing a payoff matrix, in which the victim has two choices, resist or comply, and the threatener has two, accept or punish. As a rule, a threat has a certain built-in implausibility, that of being costly — or irrational — to carry out. The threatener's problem is to make his threat sufficiently plausible to the victim. He may do so by means of four main techniques: (1) by binding himself irrevocably; (2) by putting up forfeits; (3) by making the victim unsure of what would be rational; and (4) by appearing to be irrational — or, as with Hitler, by [being] irrational. In the last analysis, however, since the estimates of payoffs — or risks — are subjective variables, the answer to successful blackmail is not within the scope of logic: it is an art.